Transformer.



T. SHAW.

TRANSFORMER.

APPLIUATIQN FILED SBPT.29.1913.

Patented Mar. 30, 1915.

- UNITED srarpsjrnur OFFICE.

THOMAS SHAW, OF HACKENSACK,' NEW JERSEY, ASSIGNOR T0 AMERICAN TELEPHONEAND TELEGRAPH COMPANY, A CORPORATION 0F NEW YORK.

TRANSFORMER.

Specification vof Letters Patent.

Patented Mar. 30, 1915.

Application led September 29, 1913. Serial No. 792,474.

To all whom t may concern:

Be it known that I, THOMAS SHAW, residing at Hackensack, in the countyof Bergen and State of New Jersey, have invented certain Improvements inTransformers, of which the following is a specification.

rl`his invention relates to electrical transformers, and especiallythose intended for use in phantom telephone circuits, its principalobjects being to provide an efficient device of this character whichshall be so balanced as to minimize crosstalk.

,I The invention is illustrated in one of its embodiments in connectionwith a system for reducing reflection losses in phantom circuits, whichis the subject of my application for Letters Patent filed February 28,1913, Serial No. 751,288, of which this application is a division.

Figure l of the drawing represents my improved transformerdiagrammatically; and Fig. 2 shows it connected in the phantom circuit.

Similar characters of reference designate like parts throughout.

In Fig. 2 appears a portion of a phantom telephone circuit consisting ofphysical circuits L, L2 with the conductors in parallel furnishing thesides of the phantom. The

physical circuits are considered to be in successive sections furnishedby connected lines or portions of a single line, these sectionspresenting different impedances. The phantom would therefore harecorresponding sections S, S', likewise different in impedance, S beingthe low and S the high impedance section. At the junction of thesesections reflection losses naturally occur.

Included in the phantom circuit between the high and low impedancesections is a reflection reducingr device consisting of my improvedtransformer U, connected in the present instance as an autotransformer.The windings u and u, u, u2, U22 of this trans-\ former may be lookedupon as bearing a bridge and series relation' to the phantom. u and u"are separately in series with the two conductors of the side circuit L',while u2, u22 are similarly included in the conductors of L2. Winding uis bridged by conductors c, c between neutral points of the sidecircuits through a suitable combination of inductances and capacities,here illustrated as in the bridge windings of autotransformers T-, T2belonging to the respective side circuits L, L2. The brid e Winding u oftransformer U, by virtue o its connection withthe said circuits, isentirely independent of operating current therein and carries onlyoperating current for the phantom, this being the difference between thecurrent in the high and low impedance phantom sections. The current insaid low impedance section does not traverse the series windings of thetransformer U, through which flows the current in the high impedancesection of the phantom, together with the operating current of theyrespective side circuits.

It is desired that the transformer U shall produce its full refiectionreducing effect upon the phantom circuit without substantial effect uponthe side circuits. end the impedance of the bridge of the phantom, whichconsists mainly of the impedance of the winding u, should approximatethe impedance of the phantom section S: and the impedance of the bridgeplus that of the series windings u, u, and u2, u should correspond tothe impedance section S. On the other hand, the side circuits should notbe materially aliected by the transformer U. The relation between thevwindings of the transformer should also be such -as to minimizeelectromagnetic and electrostatic crosstalk between the phantom and itssides and between said sides.

Referring to Fig. l, where, in addition to the letters' indicating thewindings as a whole, numerals are applied to designate the terminals, itwill be seen that the seriesl and inductance by being divided into sec-`tions each having an equal number of turns and occupying opposite halvesof the core, with the sections on each half at different' distances fromthe core; that is, one section of each pair is adjacent to the core andthe other section outside a section of the companion pair.

Over the series windings is placed the bridge winding 9 10, alsoenveloping the whole core and being in sections equally di- To thisvided between the halves of said core. lVith the elements of thetransformer in the relation shown, and considering first the phantomcircuit, the series windings of each side circuit are in parallel, withthe mutual inductance aiding the self inductances; and .taken togetherthe side circuit windings are in series with the mutual inductancebetween the pairs aiding the self inductances. Furthermore, themutualinductance between the bridge winding and all the series windingsincreases the total inductance` of the transformer for the phantom. Thereiiection reducing efiiciency of the device may be expressed by theratio of the impedance resulting from the series connection of thebridge winding 9-10 and the pairs 1 2, 3--4 and 5-(5, 7 8 of the serieswindings in inductive-aiding relation (it being remembered that each ofthese pairs of series windings considered separately is in parallelinductive'ly aiding) to the impedance of the bridge winding. As thepeculiar connection of the bridge winding prevents its iniuencing theside circuits, the only effect of the transformer upon the side circuitwill be the series opposing impedance of the series windings, which willbe equivalent to their direct current resistance only.

The careful impedance balance between the various windings of thetransformer practically eliminates electromagnetic crosstalk through itbetween the v phantom and -i'ts' sides. The twistingv of both pairs ofseries windings and the alternating of the sections give perfect mutualsymmetry with respect to the bridge winding, and of course winding.

l' portant..

By properly proportioning the yarioiisv one to the other. 'Astoelectrostatic' crosstalk, the only direct admittances vwhich can causethis and which areunsyinmetrical are v those between the outer'layersloftlie. series windings and inner'laye'rs of the bridge windings of thetransformer Ulan d,- anceratiofmay beobtained-adapting 1t any'particular values of impedance of the circuit-sections. yI will gitjethe approiimatev datafory a transformer such as hereinbefore describedhavin the ratio of 3 to l. The sections ofthe bridge winding may have1,000 turns of conductor with a direct current resistance of 8v ohms;`series windings 1--2,-34.4.; '5-6, 7-8, eacl; 365 turns with a directcurrent resistance of 4 ohms. For""the phantom circuit there will beintroduced by the transformer at a frequency of 800 cycles a seriesimpedance of 124 ohms and 0.493 henry, a4 bridge impedance of 233 AThisis comparatively unim# ohms and 0.925 henry anda mutual impedance of 163ohms and 0.67 henry. For each side circuit there will" be a series'impedance of 8 ohms and 0.001 henry.

I claim:

1. A transformer comprising a core, windings on the core consisting ofplural conductors arranged in sections on diiferent portions ofthe core,the sections being at different distances from the core, and a windingconsisting of a single conductor extending about' the entire core.

` 2. A transformer comprising a core, windings on the core consisting ofplural conductors arranged in sections on diferent portions of the core,the sections being at different distances from the core, and va windingconsisting of a single conductor extending about the entire coreoutsidethe sectional windings. i

3. A transformer comprising a core, windings on the core consisting of aplurality of pairs of twisted conductors, said pairs being balanced withrespect to resistance and inductance, and another winding consting of asingle conductor.

lSFO

4. A reflection reducing transformer comprising a toroidal core,windings on the core including a plurality of pairs of twistedconductors, each pair being in sections situated on different portionsof the core withthe sections of the lsame winding at 'differentdistances from'the core.

5. -A Atrans'former comprising a toroidal core, windings on the coref'consistig of'a plurality of pairs of twisted conductors', andanother winding cnsistingof a single conductor, they twisted windingsbeing in sections situated -on different portions of the core with-'thei canons of the same winding idierent distances'from the core and l uitIn testimony whereof, I have signed my name 'to this specification inthe presence of two subscribing 'witnesses, this twenty fifth day ofSeptember, 1913.

THOMAS SHAW.

'Viitnesses'z-9'"A I W. M. GoULD, JOHN F.' RHAME.

